This is the thread for me, oh my wow. FA Trainers are the main cards I collect above all else, so I have a lot to say here.
Past: Wally (ROS, 107/108)
The art. It's the art with this one, it's just such a beautifully illustrated card. The background is beautiful and well-done as well. Wally's growth and character throughout RSE and ORAS was executed so well, and I think the card shows his innocence.
Present: The Masked Royal (085/SM-P)
I absolutely love the art on the card, and the fact there were only 100 of it printed definitely shows how rare it is, because if anything will make people collect cards it would be that. It really sucks it was only for an event in Japan, and the high likelihood English will never see it.
Future: Ultra Recon Squad (FBL, 130/131*)
Best art on a Full-Art Trainer I have ever seen. Wally is a 2nd place to it, but nothing beats this so far. The expressions given to them match their in-game personalities so well, and the background giving off the Ultra Wormhole vibe is just perfect. I just love Zossie. <3
Dream: Wallace
One of my favorite trainers from the Pokémon games. I'm in love with his utter flamboyance and the way he's one of the few powerful trainers to be shown doing other things, such as contests with his niece, Lisia, in ORAS. I think he's a character that gives artists lots of room to show off his big personality, leaving for some really great or poor stylistic decisions with his artwork.
* - set number unconfirmed